Graham Gibbons, outside Cardiff Crown Court at an earlier hearing, was cleared of voyeurism after just 10 minutes of deliberation by the jury

In his scientific mind, the question clearly demanded an answer.

Just how long did time and motion expert Graham Gibbons spend making love to his girlfriend? And – crucially – who did what to whom and when, precisely?

There was only one way to find out. The 42-year-old specialist in time and motion engineering – the science of making businesses more efficient through studying people at work – would conduct his own evaluation.

Time wasn’t a problem. The motion part would take a little more thought.

So, he secretly rigged up a camera-phone in the bedroom, a court heard yesterday – and filmed an entire session with his unsuspecting brunette partner.

Then he downloaded the video on to a laptop – and gave a professional assessment of his performance.

Results: ‘After studying the tape, I gave her 20 minutes of satisfaction, five minutes of intercourse, and another nine minutes of sexual satisfaction,’ he told police.

A jury heard he had insisted throughout their relationship he was doing more than his fair share in the bedroom. Now, he had a 34-minute record he could use ‘to evaluate his performance’.

What Mr Gibbons failed to factor in was that his ‘outraged’ lover would discover the film – and promptly end their relationship.

The story of science versus romance unfolded at Cardiff Crown Court after Gibbons denied a charge of voyeurism, a crime under the Sexual Offences Act.

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He maintains he recorded his bedroom prowess at home in Pontypool, South Wales, as an ‘academic research’ project, and denies making the tape for sexual gratification or to show anyone.

Clear the court: Judge Nicholas Cooke asked that Cardiff Crown Court be cleared while the 35-minute X-rated sex tape was shown to jurors

Prosecutor Hywel Hughes told the hearing: ‘Gibbons set up his mobile phone which had a camera facility in his bedroom.

‘What he recorded was the private
sexual activity between both parties. Graphic sexual activity can well
be seen in that video and it lasts for some half an hour.

‘The filming was to determine who was
spending the most time doing what and an analysis of a time and motion
study. He was able to give police officers an accurate breakdown of time
spent on different activities.’

His partner, who cannot be named for legal reasons, had no idea she was being filmed.

Mr Hughes added: ‘In time and motion
studies in employment, people would be aware of what you were doing. But
this was totally covert and she did not know what was going on.’

The woman made a copy of the film and handed it to police.

When she asked Gibbons why he did it
without her permission, he is said to have told her: ‘I’m a pervert, I
get off on it.’ Judge Nicholas Cooke said it was ‘an unusual case’,
adding: ‘Gibbons described the video as time and motion analysis or
academic research.

‘He said he wanted to see what was
going on during love-making ... their sex life was boring and he was the
one doing all the work.’